I discovered this gal on my patio one morning.  In this position with her wings folded back, she was about 2.5 inches (6 centimeters) long.  Sadly, she took off after I snapped this photo, so I never did capture a better picture of her.  Still, her wonderfully unique coloration is evident even in this sub-par presentation.

[Update]: This large moth is called a leopard moth (also giant leopard moth or great leopard moth) and is scientifically known as Hypercompe scribonia.